Information may be more rapidly processed and transmitted using optical as opposed to electrical signals. Optical signals can be used to enhance the performance of electronics processors. For example, electronic wires interconnecting integrated circuits (ICs) can be replaced with optical interconnects and the information processed with IC driven electro-optic modulators. Optical signals in fiber optic communications can be encoded on the optical carrier using electro-optic (EO) modulators. In both of the processes above, nonlinear optical materials with second-order nonlinear optical activity are necessary to affect the modulation of light signal.
Nonlinear optical materials can also be used for frequency conversion of laser light. Such a conversion is desirable in many applications. For example, optical memory media presently read using 830 nm light from diode lasers. The 830 nm light wavelength limits the spot sizes which can be read and hence the density of data stored on the optical memory media. Similarly, in fiber optic communications, light wavelengths of 1.3 .mu.m or 1.5 .mu.m are desirable due to the low transmission losses of glass fiber at those wavelengths. However, those wavelengths are too long for detection by Si based detectors. It is desirable to frequency double the 1.3 .mu.m or 1.5 .mu.m wavelengths to 650 nm or 750 nm wavelengths where Si based detectors could be used.
Nonlinear optical materials which have been used in electro-optic devices have in general been inorganic single crystals such as lithium niobate (LiNbO.sub.3) or potassium dihydrogen phosphate (KDP). More recently, nonlinear optical materials based on organic molecules, and in particular polar aromatic organic molecules have been developed.
The nonlinear optical properties of organic and polymeric materials has been the subject of numerous symposia. The International Society for Optical Engineering (SPIE) has sponsored a number of NLO related symposia, e.g., the symposium "Nonlinear Optical Properties of Organic Materials II" on Aug. 10-11, 1989 (SPIE Processing Series, Vol. 1147, 1990). Similarly, the Materials Research Society has sponsored a symposium titled, "Nonlinear Optical Properties of Polymers" on Dec. 1-3, 1987 (Materials Research Society Symposium Proceedings, Vol. 109, 1988).
The organic based materials have a number of potential advantages over the inorganic and semiconductor based materials. First, the organic materials have higher NLO activity on a molecular basis. Organic crystals of 2-methyl-4-nitroaniline have been shown to have a higher nonlinear optical activity than that of LiNbO.sub.3. Second, the nonlinear optical activity of the organic materials is related to the polarization of the electronic states of the organic molecules, offering the potential of very fast switching times in EO devices. The time response of the system to a light field is on the order of 10 to 100 femtoseconds. In contrast, a large fraction of the polarizability in the inorganic crystals is due to nuclear motions of the ions in the crystal lattice, slowing the time-response of the materials. In addition, the low dielectric constant of the organic materials (e.g. 2-5 Debye at 1 MHz) compared to the inorganic materials (e.g. 30 Debye at 1 MHz) enables higher EO modulator frequencies to be achieved for a given power consumption. Third, the organic materials can be easily fabricated into integrated device structures when used in polymer form.
It is known that organic and polymeric materials with highly polarizable .pi.-electron systems can exhibit nonlinear optical (NLO) response. In many cases this response is much larger than that of inorganic substrates.
Of particular importance for conjugated organic systems is the fact that the origin of the nonlinear effects is the polarization of the .pi.-electron cloud as opposed to displacement or rearrangement of nuclear coordinates found in inorganic materials.
Accordingly, it is an object of this invention to provide novel polymers having asymmetric charge distribution.
It is another object of this invention to provide polycarbonate and polyether polymers which exhibit nonlinear optical response.
It is a further object of this invention to provide a new process for the synthesis of a polycarbonate polymer having highly polarizable .pi.-electron systems. Another object is to provide a method of making a material from such a polymer which has a non-centric alignment and which has a relatively high orientation stability. Such a material is suitable for use as a polymeric nonlinear optical component of an optical light switch and light modulator device. Accordingly, it is an object of the invention to provide laminates incorporating the NLO polymers and suitable substrates.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.